Naru Zhao

Directing the fate of human and mouse mesenchymal stem cells by hydroxyl-methyl mixed self-assembled monolayers with varying wettability

Self-assembled monolayers (SAMs) of alkanethiols on gold have been employed as model substrates to investigate the effects of surface chemistry on cell behavior. However, few studies were dedicated to the substrates with a controlled wettability in studying stem cell fate. Here, mixed hydroxyl (-OH) and methyl (-CH3) terminated SAMs were prepared to form substrates with varying wettability, which were used to study the effects of wettability on the adhesion, spreading, proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) from human and mouse origins. The numbers of adhered human fetal MSCs (hMSCs) and mouse bone marrow MSCs (mMSCs) were maximized on -OH/-CH3 mixed SAMs with a water contact angle of 40~70° and 70~90°, respectively. Hydrophilic mixed SAMs with a water contact angle of 20~70° also promoted the spreading of both hMSCs and mMSCs. Both hMSCs and mMSCs proliferation was most favored on hydrophilic SAMs with a water contact angle around 70°. In addition, a moderate hydrophilic surface (with a contact angle of 40~90° for hMSCs and 70° for mMSCs) promoted osteogenic differentiation in the presence of biological stimuli. Hydrophilic mixed SAMs with a moderate wettability tended to promote the expression of αvβ1 integrin of MSCs, indicating that the tunable wettability of the mixed SAMs may guide osteogenesis through mediating the αvβ1 integrin signaling pathway. Our work can direct the design of biomaterials with controllable wettability to promote the adhesion, proliferation and differentiation of MSCs from different sources.

Surface nanoscale patterning of bioactive glass to support cellular growth and differentiation.

Bioactive glasses (BGs) have been widely used for bone tissue regeneration as they are able to bond directly with bone. Clinical applications of these materials are likely to be in particulate form. Nanoscale materials can mimic the surface properties of natural tissues, which have exhibited superior cytocompatible property and improved tissue regeneration. The objective of this study is to prepare bioactive glass particles with nanoscale or non-nanoscale surface features and investigate their microstructure, apatite-forming bioactivity and cellular response. The microstructure and micro-nanoscale surface morphology were controlled by adding a hydroxyl-carboxyl acid (citric acid) in the sol-gel process. Results shown that the addition of citric acid induced the formation of nanoscale surface structure and increased the specific surface area, pore volume and pore size of bioactive glass particles. The citric acid with low-concentration-derived sol-gel bioactive glasses (CBGs) resulted in an enhanced apatite-formation ability in simulated body fluids (SBF) compared to normal bioactive glasses. The attachment and proliferation of rat marrow mesenchymal stem cells (RMSCs) on CBGs (low concentration) were higher than those of normal BGs, demonstrating that the CBGs had the excellent cytocompatibility. RMSCs on CBGs (low concentration) expressed the higher alkaline phosphatase activity (ALP) than normal BGs and tissue culture plastic, revealing that CBGs can induced differentiation of RMSCs to the osteogenic lineage. Such improved physical and biological properties of CBGs (low concentration) should be useful in developing new bioactive glass materials for stem cell-based bone regeneration or biomimic tissue engineering scaffolds.

Hierarchical porous hydroxyapatite microsphere as drug delivery carrier

Hollow hydroxyapatite microspheres with a hierarchical porous structure have been fabricated hydrothermally with the aid of citrate ions as a regulating agent. A possible formation mechanism was proposed. The high drug-loading capability and superior sustained release properties make it a promising carrier for drug delivery system.

Size control and biological properties of monodispersed mesoporous bioactive glass sub-micron spheres

We report a facile method for fabricating monodispersed mesoporous bioactive glass sub-micron spheres (MBGS) using dodecylamine (DDA) as a catalyst and template agent in a sol–gel process by self-assembly between a neutral organic surfactant and neutral inorganic precursor (S0I0). Moreover, we investigate the effect of sub-micron particle size on the physicochemical properties, apatite-forming ability, and biocompatibility of MBGS. Results showed that all samples exhibited regular spherical morphology and favorable mono-dispersibility. The average particle diameters of MBGS (200–800 nm) were controlled by adjusting the concentration of DDA. All samples induced the formation of rod-like apatite precipitates, which closely resembled the natural nanoscale apatite crystal, showing their high apatite-forming ability. Furthermore, MBGS surfaces also supported the attachment and promoted proliferation of alkaline phosphatase (ALP) activity of MG-63 cells, showing the good biocompatibility of MBGS. MBGS-1 had the smallest particle size and it was found that it could significantly enhance MG-63 proliferation and differentiation because of the smaller particle size and higher specific surface area. It is hoped that this study may motivate the development and applications of submicron biomaterials for bone repair applications.

Fabrication, structure and biological properties of organic acid-derived sol-gel bioactive glasses.

Sol-gel-derived bioactive glasses (BGs) have been developed for bone tissue regeneration. To develop more reliable bone tissue repair systems, it is necessary to control the morphology and surface textures of bioactive glasses. In this study, we prepared bioactive glasses by sol-gel technology using hydrochloride acid, lactic acid, citric acid and acetic acid as hydrolysis catalysts. We studied effects of acids on the morphology and surface textures, apatite-forming bioactivity and cellular response (cellular attachment and proliferation) of BGs. Results showed that the surface morphology, structure, apatite-forming bioactivity and cellular response of BG particles can be controlled by changing acid species. The hydrochloric acid-derived bioactive glass (HBG) and the acetic acid-derived bioactive glass (ABG) present high surface areas and fast apatite-forming rates. Lactic acid- and citric acid-derived bioactive glasses (LBG, CBG) exhibited nanoscale surface morphology, relatively low surface areas and comparable apatite-forming bioactivity. The results of human marrow mesenchymal stem cell (HMSC) culture exhibited that LBG and CBG have an enhanced effect on the cell proliferation, as compared to HBG, ABG and tissue culture plate. This study suggests that sol-gel bioactive glasses with proper surface textures and apatite-forming rate can affect preliminary cellular proliferation.

Effects of hydroxyapatite microparticle morphology on bone mesenchymal stem cell behavior

Understanding the shape effect of hydroxyapatite (HAp) microparticles on cellular behavior is important for enabling new kinds of biological and biomedical applications. However, it is still a challenge to prepare HAp microparticles with different shapes but similar physicochemical properties, and then to investigate their relationships with cellular behavior. Herein, we developed a novel, facile route to regulate the morphology of HAp microparticles, and investigated the interaction between the particles and bone marrow mesenchymal stem cells (BMSCs). Our results revealed that the shape of HAp has a strong influence on cellular behavior, and that the sphere-like particles performed better than the rod-like particles. These findings highlight the importance of the shape characteristics of HAp microparticles, and may provide new insights for the utility of HAp-based materials.

Surface chemistry from wettability and charge for the control of mesenchymal stem cell fate through self-assembled monolayers.

Self-assembled monolayers (SAMs) of alkanethiols on gold are highly controllable model substrates and have been employed to mimic the extracellular matrix for cell-related studies. This study aims to systematically explore how surface chemistry influences the adhesion, morphology, proliferation and osteogenic differentiation of mouse mesenchymal stem cells (mMSCs) using various functional groups (-OEG, -CH3, -PO3H2, -OH, -NH2 and -COOH). Surface analysis demonstrated that these functional groups produced a wide range of wettability and charge: -OEG (hydrophilic and moderate iso-electric point (IEP)), -CH3 (strongly hydrophobic and low IEP), -PO3H2 (moderate wettability and low IEP), -OH (hydrophilic and moderate IEP), -NH2 (moderate wettability and high IEP) and -COOH (hydrophilic and low IEP). In terms of cell responses, the effect of wettability may be more influential than charge for these groups. Moreover, compared to -OEG and -CH3 groups, -PO3H2, -OH, -NH2 and -COOH functionalities tended to promote not only cell adhesion, proliferation and osteogenic differentiation but also the expression of αv and β1 integrins. This finding indicates that the surface chemistry may guide mMSC activities through αv and β1 integrin signaling pathways. Model surfaces with controllable chemistry may provide insight into biological responses to substrate surfaces that would be useful for the design of biomaterial surfaces.

Hierarchically nanostructured hydroxyapatite microspheres as drug delivery carriers and their effects on cell viability

Hydroxyapatite microspheres (HAMSs) were fabricated via hydrothermal synthesis using propionamide (PA) as a pH-adjusting agent and trisodium citrate (TSC) as a regulating agent. Scanning electron microscopy (SEM) images indicated that the microspheres possessed well-defined 3D nanostructures constructed by nanoplates as building blocks. In vitro cell tests demonstrated that the HAMSs with or without heat treatment were able to promote the proliferation of mouse bone mesenchymal stem cells (mBMSCs). Gentamicin sulphate (GS), an anti-inflammatory, was successfully loaded in the HAMS particles at a distinctively high loading efficiency of approximately 87%. The resultant HAMS-GS delivery systems displayed a sustained release property, and the release of GS from the HAMS-B-GS500 system could significantly inhibit S. epidermidis growth. Moreover, the biocompatibility tests indicated that the HAMS-B-GS500 system exhibited excellent biocompatibility and had no toxic effects on the mBMSCs. These outstanding characteristics may make HAMSs a good candidate as an injectable and drug-loading biomaterial for in vivo tissue regeneration and drug control release.

Enhanced osteogenic differentiation and biomineralization in mouse mesenchymal stromal cells on a β-TCP robocast scaffold modified with collagen nanofibers

Calcium phosphate ceramics have been widely used in clinics as bone grafts. However, according to traditional techniques, it is difficult to create calcium phosphate bone grafts with tailored internal porous structures that may ensure optimal biocompatibility and sufficient mechanical properties. In this study, β-TCP bone scaffolds with well-defined inter-connective porous structures were fabricated by robocasting. With the aim of better mimicking the native extracellular matrix of bone without sacrificing the mechanical strength, type I collagen gel was coated on the filaments of the sintered β-TCP scaffolds to form an ultrafine fibrous network that was similar to the natural collagen nanofibers in bone. Both sintered β-TCP scaffolds and collagen gel coated scaffolds supported the growth of mouse mesenchymal stromal cells (mMSCs). Meanwhile, the thin layer of biomimetic collagen nanofibers on the β-TCP scaffolds significantly stimulated the osteoblastic differentiation of mMSCs by up-regulating the expression of ALP, Runx-2, collagen I, OPN, BSP and BMP-2. Additionally, a more active biogenesis of matrix vesicles (MVs) was induced in the mMSCs on the collagen gel coated scaffolds, evidenced by SEM and TEM results together with a significant increase of the gene expression of matrix vesicle components, indicating an enhanced initiation of matrix mineralization. Our study not only illustrates the potential use of the collagen gel coated β-TCP robocast scaffold for bone repair but also highlights the significance of the incorporation of collagen nanofibers in the scaffolds.

Characterization of bioactive ceramic coatings prepared on titanium implants by micro-arc oxidation

Abstract Micro-arc oxidation (MAO) is an enhanced chemical technology in an electrolyte medium to obtain coating structures on valve-metal surfaces. Titanium oxide films obtained by MAO in the sodium phosphate electrolyte were investigated. The films were composed mainly of TiO 2 phases in the form of anatase and rutile and enriched with Na and P elements at the surface. Their apatite-inducing ability was evaluated in a simulated body fluid (SBF). When immersing in SBF for over 30 d, a preferential carbonated-hydroxyapatite was formed on the surfaces of the films, which suggests that the MAO-treated titanium has a promising positive biological response.